1990 Vol. 14, No. 4
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Using a aerogel sample with introduced oxygen gas as a variable energy positronium source,the triplet to singlet conversion of positronium in the elastic and inelastic collisions between positronium atoms and oxygen molecules has been investigated with a time selecting energy spectrometer.We have found that the conversion cross section σ0—p is proportional to 1/v for slow positronium in the elastic collisons,where v is the mean velocity of positronium,and for the inelastic processes,the cross sections are estimated to be σ0—p=2.1×10－17cm2 and 6.6×10－18cm2 respectively at kinetic energies of positronium near two thresholds.
Through the analysis of the various factors which affect the intensity of γ-families observed by mountain emulsion chamber and the comparison of the experimental data with the results from Monte-Carlo simulation,the inference that the proton fraction in primary chemical composition at UHE region,say 1015 eV,is about 30% is proved to be acceptable.
The analysis of the data from the heavy ion experiments at SPS of CERN and BNL indicates a strong dependence on the nuclear collision geometry.In this note we develope a stochastic method to generate such a geometry by using computer with the property that the known nuclear charge distributions,the hadronic interaction cross sections and the two nucleon correlations are all accounted for in a stable framework.
We extended the MAC principle to the case for semisimple metacolor gauge group and the constructed and SO(10)×SU(4) chrial preon model which satisfies the complementarity principle.This model had a unique solution and thus predicted 4 generations of quarks and leptons without exotics.The generation gauge group was intruduced and the breaking of mass degeneracy among different generations was investigated.
Using the quark production and combination rules in e+e－ annihiation,we have calculated the ratio of charmed baryon to meson in e+e－ annihilation.The pridectied ratio is a function of energy s,and is consistent with the experiments.
Using the real time Green's function method and SGII-type interactions,we calculate the pressure,the critical temperature and other thermodynamical quantities.We compare our results with that given by other nucleon-nucleon effective interactions.
Considered the intranuclear cascade,a model for describing the distribution of grey particles in high energy hA interactions is proposed.An agreement between experimental data and the model is obtained in pA interactions and the number of grey particles could be used reasonably to measure the number of hN collision inside A.
A nuclear emulsion stack bombarded by 14.6A GeV oxygen nuclei has been analyzed.The measurement of an event of a 14.6A GeV oxygen nucleus into helium nuclei has been performed.The mechanism of the fragmentation processes has been discussed.The event provides a direct experimental evidence for the cluster model of the oxygen nuclei.
The neutron capture cross sections of Ta and In were measured in the energy range from 0.34 to 1.68MeV.A large liquid scintillator detector was used for detecting the prompt capture γ radiation.Two long-counters were used for monitoring the neutron flux.In order to reduce background the fast coincidence between the two half-spheres of the detector and the time-of-flight technique were used.The capture cross sections of Ta and In were determined relative to the standard cross section of Au.Present results were compared with others and discussed.
Based on a simplified Hamiltonian model the transition from quantum to classical diffusion behaviours for a system has been shown.The approximation of a locally harmonic oscillator and reduced density operator in the harmonic oscillator are generalized to calculate the escape tate over the barrier for the system in a fission potential consisting of a ground state well and barrier.
The influence of quantum effects on the one-body dissipation has been studied in a Monte Carlo simulation method.The results show that the influence of quantum effects decreases and finally dissappears as the frequency and amplitude of the collective oscillation increases.The wall formula with quantum effect taken taken into account to some extent is given analytically.
The characteristic dilepton mass distributions from the decay of high temperature-density quark-gluon matter in ultrarelativistic nucleusnucleus collisions were calculated via the relativistic hydrodynamics.Both longitudinal expansion accompanying transverse expansion of the matter and the effect of phase transition leading to the re-distribution of the temperature were considered.The characteristic phenomena which have been suggested as a test for the existence of quark-gluon plasma were given and provided as a theoretical basis of experiment.
The cross sections of the neutron induced (n,2n) reaction an the unstable target nucleus 88Y in the energy range from 10.3 to 17.4MeV are obtained from the measurement of the 87Sr (d,2n) reaction.This work is based on the hypothesis that the formation of the Compound nucleus is independent of its decay.The results are compared with our calculated results and the experimental data and calculated result of Prestwood and his co-worker.The comparison indicates that this work is worthy for further study.
The ground state Potential Energy Surface for nucleus 190Hg was calculated in terms of Nilsson-Strutinsky method with standard κ,μ set and modified one.It is shown that there is a low-lying second minimum in prolate side except the known oblate minimum.The existence of such a prolate minimum,which is different from Total Routhian Surface calculation,may explain the recent observation of extra deformation band in 190Hg.
A(1+1)-dimensional lattice U91) gauge model with fermion species doubling is solved exactly.The results show that doubling exists for meson states composed of fermions and antifermions.Furthermore we prove that Susskind fermions can beat the doubling of meson states.
Various E1 transition rates for cc states are calculated in a QCD-motivated potential model.Relativistic corrections are found to be substantial.While a good agreement between theory and experiment is achieved for the rates of ψ(2s)→γχcJ and χcJ→γψ(1S)(J=0,1,2),the calculated rates for ψ(3770)→γχcJ are smaller by a factor of～2 than their experimental values obtained by the MarkⅢ collaboration.The effect of the 23S1—13D1 mixing is possibly important and needed to be considered.
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